1. Field of the Invention
This invention relates to injection moldable and extrusion type elastomeric compositions having a viscosity at 200.degree. C. at 0.73 sec.sup.-1 of less than about 8.times.10.sup.5 poises. The compositions used for elastomeric articles include 100 parts of a neutralized sulfonated EPDM terpolymer; about less than 200 parts per hundred of a paraffinic, low polarity process oil; about 25 to about 200 parts per hundred of an amorphous silica filler; and a preferential plasticizer at about less than 50 parts per hundred based on 100 parts of the sulfonated elastomeric polymer. The composition may also include a crystalline polyolefinic thermoplastic at less than about 100 parts per hundred by weight per 100 parts of sulfonated polymer.
These blend compositions can be readily processed due to their superior rheological properties on conventional plastic fabrication equipment, especially on low and high pressure injection molding or extrusion equipment into elastomeric articles having excellent physical properties and desirable rubbery characteristics.
2. Description of the Prior Art
Recently a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728, herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically crosslinked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature. However, these ionically crosslinked elastomers may be processed like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations of the elevated temperatures thereby creating a reprocessable elastomer.
The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from Groups I, II, III, IV, V, VIB, VIIB and VIII and mixtures thereof of the Periodic Table of Elements. Although these sulfonated elastomeric polymers prepared by the process of this patent are readily usable in a certain number of limited applications, they are not as readily adaptable for the manufacture of an injection moldable elastomeric article such as footwear or extrusion articles such as garden hose as are the improved compositions of the present invention, wherein both improved physical and rheological properties are realized.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines. The resultant ionically crosslinked sulfonated elastomers prepared by this process do not exhibit both the improved physical and rheological properties of the compositions of the present invention.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. F. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reverisbly disrupts the association of the sulfonate groups at a temperature of forming. The compositions formed by this process are not as suitable for the manufacture of high performance elastomeric articles such as footwear formed by an injection molding process or garden hose by an extrusion process as are the compositions of the present invention.
U.S. Pat. No. 3,847,854, herein incorporated by reference, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debye, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer. Again, the compositions of the present invention are more adaptable for use in the manufacture of high performance elastomeric articles.
Products resulting from the aforementioned methods for obtaining neutralized sulfonated elastomeric compositions possess either unsuitable rheological or physical properties for the applications envisioned in the present invention.
For example, the balance of physical and rheological properties of these resultant sulfonated elastomeric products of these aforementioned patents are unsuitable for major applications of injection molding or extrusion processes, for example the manufacture of footwear or garden hose, wherein excellent resilience, dimensional stability, excellent low and high temperature flexibility, excellent flex fatigue, and excellent abrasion are needed. Furthermore, the high melt viscosity and melt elasticity of these materials makes injection molding and extrusion difficult if not impossible. These materials of the aforementioned patents which are generally processable by only compression molding have unsuitable physical properties for such major applications as footwear and garden hose.
The materials cost of the compositions of the instant invention is substantially reduced over those of the aforementioned patents, wherein these previous patents failed to realize the criticality of the proper selection of the chemical and physical uniqueness of the basic elastomeric backbone, the degree of sulfonation, the proper selection of neutralizing agent in conjunction with plasticization, and the ability to extend these sulfonated polymers with oils and fillers. Unsulfonated elastomers, when extended with oils and fillers, show a general deterioration in physical properties. Quite surprisingly, through the proper selection of oil and a specific type of filler within a critical ratio of filler to oil, the sulfonated elastomeric compositions of the present invention show a marked improvement in both rheological and physical properties.
U.S. Pat. Nos. 3,974,240 and 3,974,241 filed on Nov. 18, 1974, describe the blending of a crystalline polyolefinic material with a neutralized sulfonated elastomeric polymer in an attempt to improve both the rheological and physical properties of the elastomeric polymer. The selection of the use of the crystalline polyolefinic material to improve both the stiffness as well as improving the melt viscosity of the composition was based in part upon the limitation of the use of fillers such as carbon black, clays, calcium carbonate or silicates as a single additive to the elastomeric polymer. Although fillers in combination with an elastomeric polymer increase the hardness of the composition, these fillers deteriorate the melt viscosity of the resultant composition. These materials are more adaptable for stiff elastomeric articles such as rubberized chair tips or wheels whereas the compositions of the present invention are more adapted for flexible elastomeric articles such as elastomeric footwear.
The unique and novel improved compositions of the present invention overcome the deficiencies of the aforementioned U.S. patents and applications from both a rheological and physical aspect. The blend compositions of the present invention solve the problem of having a material which has both desirable rheological and physical properties for the manufacture of an elastomeric article as an elastomeric footwear or garden hose, wherein the extrudate of the resultant compositions do not exhibit melt fracture during extrusion processing as in the case in some of the aforementioned patents. Additionally the improved compositions of the instant invention provide systems having improved adhesion and surface shine.